Engine control systems utilize a measurement of exhaust gas to maintain an average air to fuel (air/fuel) ratio around a desired value. When two state exhaust gas oxygen sensors are used, a typical result is a fluctuation, or oscillation, of the exhaust air/fuel ratio around the desired value. When the exhaust system includes a conventional three way catalytic converter, these oscillations are beneficial to reducing regulated emissions.
In systems where the engine contains dual cylinder banks, each coupled to separate catalytic converters, and each bank is capable of independent air fuel control, the oscillations of the exhaust air/fuel ratio are made to be in phase of one another. By maintaining the oscillations in phase, the catalytic converter efficiency is increased and regulated emissions are reduced. Such a system is disclosed in U.S. Pat. No. 5,511,377.
In systems where the engine contains dual cylinder banks each coupled to separate catalytic converters, and each bank is capable of independent air fuel control, the oscillations of the exhaust air/fuel are made to be out of phase of one another. By maintaining the oscillations out of phase, torque fluctuations are minimized with no efficiency effect on either of the two catalytic converters. Also, because there are two separate catalytic converters, the relative phase does not effect emissions. Such a system is disclosed in U.S. Pat. No. 5,462,038.
The inventors herein have recognized numerous problems with the above approaches. For example, in systems containing a dual bank engine connected to a single catalytic converter, idle quality is severely effected by the torque fluctuations when the air/fuel ratio of each bank is forced to oscillate in phase. Further, a system containing two catalytic converters is much more costly to manufacture and produce, thus lowering customer value.